Project 3 Freshly ejaculated mammalian sperm are unable to fertilize an egg. They acquire fertilizing capacity in the hours following ejaculation, as they pass through the female reproductive tract, in a process known as capacitation. Soluble adenylyl cyclase (sAC: ADCY10) is a non-hormonal target essential for sperm capacitation and male fertility. Pharmacological sAC inhibitors block sperm functions in vitro and two distinct sAC knockout (KO) mouse strains exhibit male-specific sterility without exhibiting other overt phenotypes. The overall hypothesis tested in this Contraception Research Center (CRC) is that sAC inhibitors can be designed which can be appropriately dosed to block sperm functions while minimizing undesirable side effects. We have recently identified small molecule activators of sAC which function via regulatory domains outside sAC?s catalytic core. These activators selectively stimulate isoforms of sAC enriched in sperm. In this Contraception Development Research Project, we hypothesize that a new class of inhibitors, which binds to these regulatory domains, will prevent capacitation by selectively inhibiting sAC functions in sperm. Regulatory-domain targeting sAC inhibitors would produce fewer undesirable side effects. In this Project, we propose a high throughput strategy to identify small molecules which block the activation of sperm sAC and prevent capacitation. Suitable regulatory domain sAC inhibitors will be subjected to the pipeline of refinement cycles and in vivo studies described in Projects 1 and 2 of this CRC. The ultimate goal of this Project is to develop inhibitors selective for sAC isoforms in sperm as lead compounds for oral, non-hormonal contraceptives.